EP2700962B1 - Measurement of a resistance of a switch contact of an electrical circuit breaker - Google Patents

Description

The present invention relates to a method and a device for measuring a resistance of a switching contact of an electrical circuit breaker, and to a method and a device for measuring resistances of switching contacts of an electrical circuit breaker arranged in a series circuit. In particular, the present invention relates to a measurement of contact resistances of the closed switch contact or the closed switch contacts of the electrical circuit breaker.

Circuit breakers, also referred to as high voltage switches, circuit breakers or circuit breakers, are used in power engineering to make or break electrical connection under load. The rated voltages of the circuit breakers can range from a few volts to a few hundred kilovolts. The switched load currents can amount to tens of kiloamps in the event of a short circuit. For reliable operation of the circuit breaker, the contact resistance of a switching contact or a plurality of series-connected switching contacts of the electrical circuit breaker is therefore checked, for example in the context of revisions.

Circuit-breakers for medium-voltage systems usually have only one switching contact, which can be opened or closed. Circuit-breakers in high-voltage and extra-high voltage installations can comprise a plurality of switching contacts, so-called breaker units, in a series connection. In the series or series connection of multiple interrupter units, capacitors with a size in the range of a few picofarads are generally arranged parallel to the individual interrupter units in order to distribute the voltage evenly across the individual interrupter units. Multiple breaker units in one phase of a circuit breaker are generally opened or closed simultaneously.

For circuit breakers, the resistance measurement at the closed switching contact, which is also referred to as a micro-ohm measurement, a Standard method for assessing the quality or wear of the circuit breaker.

In this context, the publication of " NILS WÄCKLEN et al: "High voltage circuit breaker testing with dual grounding", ENERGIZE, No. May 2008, May 1, 2008 (2008-05-01), pages 52-55, XP055054228 The method performs a circuit breaker timing test with both sides being grounded throughout the test In the test method, a contact resistance is measured by measuring the current through the earth The earth loop current is measured with current clamps which provide sufficient accuracy.

The micro-ohm measurement is usually carried out, for example, by impressing a high direct current of 100 amps across the closed switch contact. The current is fed in via current terminals, which are clamped on both sides of the circuit breaker to the conductors leading away from the circuit breaker. With other terminals, the voltage is also tapped on both sides of the circuit breaker. The voltage terminals are usually mounted closer to the switching contact of the circuit breaker and thus carried out a so-called four-wire measurement. This can be prevented that the voltage drop is measured along with the current terminals, whereby the measurement result would be falsified. From impressed current and measured voltage, the resistance of the closed switch contact, including the resistance of the supply lines from the voltage terminals to the switching contact can be determined. Alternatively, instead of separate current and voltage terminals, so-called Kelvin clamps can be used. In Kelvin clamps, two jaws of each terminal are electrically isolated from each other and one of the two jaws feeds the current and the other of the two jaws picks up the voltage. The advantage of these Kelvin clamps is that only one clamp is to be clamped on each side of the circuit breaker.

For micro-ohm measurement, as described above, a current source and a voltmeter can be used, so that voltage measurements on the various switch contacts can be performed one after the other. It is also possible to use a plurality of voltmeters, with the current being impressed with a common current source via a plurality of contacts and with the plurality of voltmeters being able to determine several voltage values at the same time.

Since in power engineering plants, for example in a substation, dangerously high voltages can occur in many places, it is necessary to earth the circuit breaker during this micro-ohm measurement. For example, the circuit breaker on both sides of the rest of the power grid can be separated and grounded on one side. The micro-ohm measurement can then be carried out precisely when the switch contact or closed switch contacts are closed. Frequently, further measurements are to be performed on the circuit breaker, in which the switching contact must be open at least temporarily, for example, a measurement of the time that the switch needs to open. In such measurements, a two-sided grounding of the switch is recommended in order to avoid a hazard to persons performing the measurement. For the micro-ohm measurement, therefore, one of the two groundings will be removed for the duration of the measurement, but this is very cumbersome, or the micro-ohm measurement will be faulty if grounded at both ends by the parallel earth loop.

In order to perform a micro-ohm measurement on a circuit breaker efficiently, the circuit breaker can be grounded on both sides and with a DC current clamp or a shunt, the proportion of current flowing from the power source through the grounding sets, be determined and used to correct the measured resistance. Although this method is very accurate, it has the disadvantage that additional measurements using the current clamp or shunt are required.

The object of the present invention is therefore to enable an efficient resistance measurement or micro-ohm measurement for one or more switching contacts of an electrical circuit breaker, wherein a risk to personnel carrying out the resistance measurement should be largely avoided.

This object is according to the present invention by a method for measuring a resistance of a switch contact of an electric circuit breaker according to claim 1, a device for measuring a resistance of a switch contact of an electrical circuit breaker according to claim 6 and a test environment for measuring a resistance of a switch contact of an electrical circuit breaker after Claim 8 solved. The dependent claims define preferred and advantageous embodiments of the invention.

According to the present invention, there is provided a method of measuring a resistance of a switching contact of an electric circuit breaker. In the method, a first resistance across the circuit breaker is determined while the circuit breaker is grounded on both sides and the switch contact is closed. Furthermore, a second resistance across the circuit breaker is determined while the circuit breaker is grounded on both sides and the switch contact is open. In response to the first resistance value and the second resistance value, the resistance of the closed switch contact is determined. Earthing on both sides can be achieved, for example, by two grounding sets from ground to the corresponding conductors. Alternatively, the grounding may be performed by means of a grounding set that is connected to ground only once and has several terminals that can be earthed. The first resistance value when the switch contact is closed corresponds to a resistor of the parallel circuit consisting of a closed switch and ground. The second resistance value corresponds to the grounding resistance. The resistance of the closed switch contact R _switch can be determined, for example, by the following equation: $${\mathrm{R}}_{\mathrm{switch}}=\frac{{\mathrm{R}}_2•{\mathrm{R}}_1}{{\mathrm{R}}_2-{\mathrm{R}}_1}$$

Where R _{1 is} the first resistance value and R _{2 is} the second resistance value. Since the wiring does not have to be changed between the two measurements, the measurement can be carried out very accurately.

In one embodiment, the first and second resistance values are each determined by impressing a DC current into the double-ended circuit breaker and measuring a voltage across the circuit breaker. Thus, conventional micro-ohm measuring devices can be used for determining the first and second resistance values.

The circuit breaker may include a three-phase switch. Each phase is assigned at least one switching contact. Three-phase switches can include one common or three separate drives. In some three-phase switches and individual phases can be switched individually, for example, in cases where an error occurs only at one phase and thus only the shutdown of a phase is necessary. The method described above can be applied individually for each phase and is therefore also suitable for multi-phase circuit breakers. The method can also be performed simultaneously on two or more phases, whereby a check of a multi-phase switch can be performed efficiently. According to a further embodiment, the power switch may comprise a maximum high or medium voltage switch. Since the process is independent of the circuit-breaker voltage to be switched, it can be used for medium-voltage switches with a rated voltage of, for example, 1 kV - 45 kV, a high-voltage switch with a nominal voltage of 45 kV - 150 kV or a maximum voltage switch with a rated voltage of more than 150 kV become.

According to the present invention, there is further provided an apparatus for measuring a resistance of a switching contact of an electric circuit breaker. The device comprises a drive unit for driving the electrical circuit breaker to selectively open or close the switching contact of the circuit breaker. The device further comprises a Resistance measuring device, which can be coupled to the drive unit and the circuit breaker. The resistance measuring device is capable of determining a first resistance across the circuit breaker while the circuit breaker is grounded on both sides and the circuit breaker switching contact is closed. The resistance measuring device is further able to determine a second resistance across the circuit breaker while the circuit breaker is grounded on both sides and the switching contact is open. In dependence on the first resistance value and the second resistance value, the resistance measuring device determines the resistance of the closed switching contact. In particular, when the resistance measuring device is coupled to the drive unit for opening and closing the switching contact of the circuit breaker, the resistance measurement can be carried out fully automatically. For example, after connecting the resistance measuring device to the electrical circuit breaker and grounding the circuit breaker on both sides, the switching contact of the circuit breaker is automatically closed, then the first resistance value is measured and then, after the switching contact has been opened automatically, the second resistance value is measured. Finally, the resistance measuring device can determine and output the resistance of the switching contact according to the equation described above.

The device may also be designed to carry out the method described above or one of its embodiments, and therefore also comprises the advantages described above.

According to the present invention, there is further provided a test environment for measuring a resistance of a switching contact of an electric circuit breaker. The test environment includes the circuit breaker, first and second grounding sets, and a resistance measuring device. The first grounding set is coupleable to a first side of the circuit breaker to ground the first side of the circuit breaker. The second grounding set can be coupled to a second side of the circuit breaker to ground this second side. The resistance measuring device can be coupled to the two sides of the circuit breaker in such a way that a resistance value can be determined by means of the resistance measuring device can be determined across the circuit breaker, while the circuit breaker is grounded on both sides and the switching contact is closed, and a second resistance across the circuit breaker is determined while the circuit breaker is grounded on both sides and the switching contact is opened. With the aid of the resistance measuring device, the resistance of the closed switching contact can furthermore be determined as a function of the first resistance value and the second resistance value.

• Fig. 1 zeigt eine Testumgebung mit einem beidseitig geerdeten elektrischen Leistungsschalter und einer Vorrichtung zur Messung eines Widerstands eines Schaltkontakts des Leistungsschalters gemäß einer Ausführungsform der vorliegenden Erfindung.
• Fig. 2-4 zeigen Testanordnungen mit Vorrichtungen zur Messung von Widerständen von Schaltkontakten von elektrischen Leistungsschaltern, welche jedoch keine Ausführungsformen der vorliegenden Erfindung darstellen.

The present invention will be explained below with reference to the accompanying drawings with reference to preferred embodiments.

• Fig. 1 shows a test environment with a double-ended electrical circuit breaker and a device for measuring a resistance of a switching contact of the circuit breaker according to an embodiment of the present invention.
• Fig. 2-4 show test arrangements with devices for measuring resistances of switching contacts of electrical circuit breakers, which, however, do not represent embodiments of the present invention.

Fig. 1 shows a test environment 10 with a power switch 11, which selectively connects or disconnects a first high voltage line 12 to a second high voltage line 13. The test environment 10 further includes a first grounding assembly 14 coupled to a first side of the power switch 11 and a second grounding assembly 15 coupled to a second side of the power switch 11. By the two-sided grounding of the circuit breaker can ensure that no dangerously high voltages applied to the circuit breaker 11. The test environment 10 further comprises a Mikroohmmessvorrichtung 17, which is coupled via four connections 24-27 with the two sides of the circuit breaker 11. The circuit breaker 11 comprises an electrical switching contact 16, which can be selectively opened or closed by means of a control drive 19 and a mechanical coupling 18, to establish or interrupt a connection between the lines 12 and 13. The control drive 19 can be controlled, for example via a control line 28 to open the switch contact 16 or close. In addition, the control drive 19 can be manually controlled or actuated by an operator to selectively open or close the switching contact 16.

The device 17 comprises a resistance measuring device which comprises, for example, a current source 23 and a voltmeter 22. The current source 23 impresses a current I through the power switch 11 and the two-sided grounding 14, 15 via the connections 24, 25 and the voltmeter 22 detects a voltage drop V across the connections 26, 27 across the power switch 11. The device 17 further comprises a Processing unit 20, which calculates a resistance across the power switch 11 in dependence on the current I impressed by the current source 23 and the voltage V measured by the voltage meter 22 voltage. The processing unit 20 is further coupled to a drive unit 21 of the device 17, which activates the control drive 19 of the power switch 11 via the connection 28. Thus, the processing unit 20 is able to selectively open or close the switch contact 16. The operation of the device 17 will be described below.

The circuit breaker 11 is earthed by means of the grounding sets 14 and 15 on both sides. The resistance measuring device 22, 23 is, as in Fig. 1 represented connected to the power switch 11, that a resistor across the power switch 11 is measurable. Then two resistance values are determined one after the other. A resistance value R ₁ is determined when the switching contact 16 is closed and a resistance value R ₂ is determined when the switching contact 16 is open. The resistor R ₁ corresponds to a parallel circuit of the resistor of the switching contact 16 and the ground loop on the ground sets 14, 15, and the resistor R ₂ corresponds only to the resistance of the ground loop on the ground sets 14, 15 using the equation described above may be made of these resistances of the resistance of the closed switch contact 16 are calculated. This is done by the processing unit 20. The processing unit 20 can also selectively open or close the switch contact 16 via the control unit 21 and therefore perform the two resistance measurements in turn once with the switch contact 16 open and once with the switch contact 16 closed, and then calculate the resistance of the closed switch contact 16 therefrom. An order in which the two resistance measurements are performed is arbitrary. Alternatively, the processing unit 20 can instruct a user via a corresponding display to open or close the switching contact 16 manually or via a corresponding actuating device if an automatic control via the drive unit 21 and the connection 28 is not provided. Since the circuit breaker 11 is grounded on both sides during the entire measurement, it can be ensured that no dangerously high voltages are applied to the circuit breaker 11.

Fig. 2 shows a further test environment 50 with a power switch 51, which comprises two switch contacts 56 and 57. The switching contacts 56 and 57 are arranged in a series circuit. The power switch 51 may comprise further switching contacts, which are arranged together with the switching contacts 56 and 57 in a series circuit. The switching contacts 56 and 57 and the optional further switching contacts are generally open or closed at the same time by means of an actuator, not shown. The power switch 51 is connected to power lines 52 and 53 coupled, which can be selectively connected or disconnected via the switch contacts 56, 57. The test environment 50 further includes two grounding sets 54 and 55 connecting the high voltage lines 52 and 53, respectively, to ground. Furthermore, in the test environment 50, a device 58 for measuring the resistance of the switching contacts 56 and 57 is shown. The device 58 comprises a first resistance measuring unit, which comprises a voltmeter 60 and a current source 61, and a second resistance measuring unit, which comprises a voltmeter 66 and a current source 67. The first resistance measuring device 60, 61 is connected via connections 62-65 to the first switching contact 56 in such a way that a current I _{1 of} the current source 61 can be impressed via the switching contact 65 when the switching contact 56 is closed. The voltmeter is connected via the connections 64 and 65 to the switching contact 56 such that a voltage drop U ₁ across the switching contact 56 can be measured. The second resistance measuring device 66, 67 is comparable to the first resistance measuring device 60, 61 coupled to the switching contact 57 via connections 68-71 for impressing a current I ₂ through the closed switching contact 57 and measuring a voltage drop U ₂ on the switching contact 57. A processing unit 59 is connected to the resistance measuring devices 60, 61 and 66, 67, respectively. The operation of the device 58 will be described below.

The high voltage lines 52, 53, which are connected to both ends of the circuit breaker 51, are connected to ground via the grounding fittings 54, 55. The device 58 is connected to the switching contacts 56 and 57 as described above. The switch contacts 56 and 57 are closed. From the current source 61 a current I ₁ is impressed on the high-voltage line 52nd The current I ₁ therefore flows in part as current I _S1 from left to right through the closed switching contact 56 and to another part as current I _E1 via the grounding set 54 to earth. The current source 67 impresses a current I ₂ on the high voltage line 53. The current I ₂ flows partly as current I _S2 from right to left through the closed switching contact 57 and to a further part as current I _E2 through the grounding set 55 to earth. Due to the contact resistance of the switching contact 56, a voltage drop U ₁ occurs across the switching contact 56. Likewise, due to the Transition resistance of the switching contact 57, a voltage drop U ₂ on the switching contact 57 on. Since the currents I _S1 and I _S2 are fed in opposite directions, the voltage drops U ₁ and U _{2 are} also oppositely directed. If the contact resistances of the switching contacts 56 and 57 are substantially equal and moreover the currents I ₁ and I ₂ are substantially equal, the voltage drops U ₁ and U _{2 are} also equal in magnitude. As a result, the voltage drop U _E across the ground loop is zero, so that the currents I _E1 and I _E2 are also zero. In this case, the current I _S1 through the switching contact 56 corresponds to the current I ₁ so that the contact resistance of the switch contact 56 U ₁ can be determined solely as a function of the current I ₁ and the temperature measured by the voltage meter 60 voltage. Likewise, the contact resistance of the closed switch contact 57 can be determined solely on the basis of the current I ₂ , which in this case corresponds to the current I _S2 , and the voltage U ₂ measured by the voltmeter 66. Since the switch contacts 56 and 57 are generally identical in construction and subject to the same load, they generally have the same contact resistance in the closed state, so that the conditions described above are met and for this so-called symmetrical case, a simple and accurate determination of the contact resistances is possible , The processing unit 59 may determine and output the corresponding resistance values based on information from the resistance measuring devices 60, 61 and 66, 67. In the event that the contact resistances of the switching contacts 56 and 57 are of different sizes, the control device 59 can adjust the currents I ₁ and I ₂ such that the voltage drops U ₁ and U ₂ are substantially equal in magnitude. This ensures that even in this non-symmetrical case, the voltage U _E across the ground loop is substantially zero and thus the contact resistance of the individual switching contacts 56 and 57 based on the current I ₁ or I ₂ and the voltage drops U ₁ and U ₂ can be determined.

Fig. 3 FIG. 5 shows another test environment 50, which essentially corresponds to the test environment 50 of FIG Fig. 2 corresponds and moreover comprises two additional switches 72 and 73, which are arranged parallel to the switching contacts 56 and 57, respectively. This makes it possible that even with open switch contacts 56 and 57, respectively a current through the ground loop, which is implemented via the grounding sets 54 and 55, can be driven in order to determine the resistance of the earth loop can. The resistance of the earth loop can then be used to correct resistance values, which are determined when the switch contacts 56, 57 are closed. In other words, with the help of the switches 72, 73 also in the Fig. 3 shown arrangement in connection with Fig. 1 described method are performed. For example, the switch 73 can be closed and the switch 72 can be opened. A micro-ohm measurement of the switch contact 56 may then be made using the resistance measuring device 60, 61 as previously described with reference to FIG Fig. 1 be described described. With the switch 72 closed and the switch 73 open, a resistance measurement device 66, 67 can be used to make a micro-ohm measurement on the switch contact 57 as previously described with reference to FIG Fig. 1 be described described.

Fig. 4 FIG. 2 shows a test environment 50, which essentially corresponds to the test environment 50 of FIG Fig. 2 equivalent. In addition, the test environment 50 includes the Fig. 4 a third grounding assembly 74 that couples a point between the switch contact 56 and the switch contact 57 to ground. In this arrangement, by means of the resistance measuring device 60, 61, a micro-ohm measurement of the switching contact 56 as with reference to Fig. 1 previously described. Likewise, by means of the resistance measuring device 66, 67, a micro-ohm measurement of the switching contact 57 as previously with reference to Fig. 1 be described described. The two Mikroohmmessungen to the switch contacts 56 and 57 can be performed simultaneously. By virtue of this additional grounding 74, it can further be ensured that no high voltage is applied between the switching contacts 56 and 57.

Claims (8)

1. A method for the measurement of a resistance of a switching contact of an electrical circuit breaker, comprising:

   - determining a first resistance value across the circuit breaker (11) while the circuit breaker (11) is grounded at both sides and the switching contact (16) is closed, characterized in that the method further comprises:

   - determining a second resistance value across the circuit breaker (11) while the circuit breaker (11) is grounded at both sides and the switching contact (16) is open, and

   - determining the resistance of the closed switching contact (16) on the basis of the first resistance value and the second resistance value.
2. The method according to claim 1, wherein the determining of the first and second resistance values respectively comprises:

   - impressing a direct current in the circuit breaker (11) which is grounded at both sides, and

   - measuring a voltage across the circuit breaker (11).
3. The method according to claim 1 or claim 2, wherein the circuit breaker (11) comprises a three-phase switch, each phase being assigned to a switching contact.
4. The method according to any one of the preceding claims, wherein the method is simultaneously carried out for a plurality of switching contacts of the circuit breaker.
5. The method according to any one of the preceding claims, wherein the circuit breaker (11) comprises an ultra-high voltage switch, a high voltage switch, or a medium voltage switch.
6. An apparatus for the measurement of a resistance of a switching contact of an electrical circuit breaker, comprising:

   - a resistance measurement device (20, 22, 23) which is configured to determine a first resistance value across the circuit breaker (11) while the circuit breaker (11) is grounded at both sides and the switching contact (16) is closed,

   characterized in that the apparatus further comprises:

   - a control unit (21) for controlling the electrical circuit breaker (11) to selectively open or close the switching contact (16) of the circuit breaker (11),

   wherein the resistance measurement device (20, 22, 23) is configured to be coupled to the control unit (21) and is configured to determine a second resistance value across the circuit breaker (11) while the circuit breaker (11) is grounded at both sides and the switching contact (16) is open, and to determine the resistance of the closed switching contact (16) on the basis of the first resistance value and the second resistance value.
7. The apparatus according to claim 6, wherein the apparatus (17) is configured to carry out the method according to any one of claims 1-5.
8. A test environment for the measurement of a resistance of a switching contact of an electrical circuit breaker, comprising:

   - the circuit breaker (11),

   - the apparatus according to claim 6 or claim 7,

   - a first grounding device (14) which is configured to be coupled with the circuit breaker (11) for grounding a first side of the circuit breaker (11),

   - a second grounding device (15) which is configured to be coupled with the circuit breaker (11) for grounding a second side of the circuit breaker (11).

Images